1. Field of the Invention
This invention relates to the purification of waste waters, particularly industrial waste waters. This invention is particularly directed to the purification of waste waters used in the Oxo-process whereby the waters are purified to such an extent that they can be discharged into waterways without adversely affecting the biological life therein. More especially, this invention relates to the purification of waste water and the separation of the same from light water insoluble organic liquids and water insoluble solids which flocculate in the presence of such water insoluble liquids.
2. DISCUSSION OF THE PRIOR ART
Specifically lighter organic compounds have generally been separated from waste waters originating from industrial plants by means of known gravity separators. Recently, it has been found that newly available tilted plate separators designed in the form of a U-tube are especially well suited. These tilted plate separators are provided with an inlet for the waste water to be treated at one side and an overflow for the purified waste water on the other. A suitable tilted plate separator is shown in an article in Oil and Gas Journal, Dec. 14, 1970, the disclosure of which is hereby incorporated herein by a reference.
Water passing from one leg of the U-tube to the other is caused to flow through a plate pack which is the purifying section of the separator. In this purification section the plates are mounted parallel to one another in a relative short distance and they are arranged at an angle of about 45.degree. to the horizontal in the direction of the flow of the waste water. The flow of the water between the plates is laminar. The settling distance is reduced to the vertical distance between the plates so that the specifically lighter organic impurities, after a short distance, meet on a wall. When they meet at the wall the droplets are united and, by virtue of the difference between their specific weight and that of water, they rise opposed to the flow direction of the water. They are caused to ride up in the free space above the plate pack. A special embodiment of a rapid gravity separator is provided with corrugated plates, the axes of the wave crests and troughs being arranged in the flow direction of the water.
Industrial waste waters being discarded must meet demands of purity in order to prevent extreme pollution of waterways, resulting in detrimental influence on the biological environment. An economic process for a complete purification with respect to a feasible apparatus in terms of assembly and financial expenditure is, therefore, highly desirable.
The separators heretofore provided have been used in separating and purifying waste waters containing easily separable specifically lighter phases as for instance specifically lighter oils and relatively coarse, quickly settling specifically heavier solids, as for instance sand.
A particular problem is encountered where the purification of the waste water involves the separation of specifically heavier solid substances of large surface area having been precipitated and being able to adsorb said specifically lighter organic liquids. In this case, small amounts of heavy sedimentary sludge, consisting for instance of metal oxides are formed besides larger amounts of voluminous layers of specifically lighter swimming sludge consisting of solid material and organic oil constituents the weight of the resultant swimming sludge being lower than that of water. It rises countercurrent to the direction of flow of the water rides up and is separated at the surface of the introduction zone or bay of the gravity separator, while the sedimentary heavy sludge separates out, descends in the tilted plate pack and settles in a collecting vessel located below the plate pack.
During the residence time of the waste water in the separator required for the separation of the voluminous floating sludge, the waste water is cooled. Owing to said cooling, resulting in a shifting of the saturation degree, a consecutive flocculation occurs in conventional separating devices. From exhaustive tests it has been observed that the solid particles precipitated and flocculated by said consecutive flocculation are extremely voluminous and settle only very slowly. Owing to their large surface area, they are capable of adsorbing the oil droplets of the organic liquid riding up in the ridges of the plates of the plate pack, resulting in the formation of a mixed solid/oil phase whose specific weight is considerably near to that of the water. Thus, the resultant phase is drifted along and discharged with the waste water. There is not formed a separate, definite and definable swimming sludge nor is any sedimented heavy sludge created within the separation zone of the gravity separator. The result is that the waste water removed from the gravity separator contains a high content of organic liquids which is mixed with the solids as sludge in an almost homogeneous phase inseperable from waterphase. Thus, the ability of the gravity separator to separate such components is considerably decreased.
It is, therefore, an object of the present invention to increase the efficiency of commercially available gravity separators for the removal of purified waste waters, especially to increase the purification efficiency of gravity separators of the parallel plate interceptive type, separating waste waters from water insoluble organic liquids of lighter weight than water and solids of large surface area which can flocculate in the presence of such lighter organic liquids, which solids are themselves heavier than water.